Means for energizing thermionic tubes



Oct. 18, 1932. w. VAN B. ROBERTS 1,882,920

MEANS FOR ENERG'IZING THERMIONIC TUBES Filed Feb. 11. 1928 2 30 as I 52 31 INVENTOR WALTER VAN B. ROBERTS A ORNEY Patented Oct. 18, 1932 UNITED STATES PATENT OFFICE WALTER VAN B. ROBERTS, or PRINCETON, NEW ERSEY, AssIG voR r RAnIo coRro- RATION or AMERICA, A CORPORATION or DELAWARE MEANS FOR ENERGIZING THERMIONIC TUBES Application filed February 11, 1928. Serial No. 253,545.

This invention relates to a means for energizing thermionic devices and especially to a means for supplying plate, filament and grid potentials to a thermionic tube from a variable or fluctuating direct current source.

The present tendency towards energizing thermionic tubes is to energize the tubes, that is, to supply plate potentials, from a source of alternating current which has been-rectified but not perfectly filtered or from a source of commutated direct current. The unidirectional current so obtained is not constant and smooth and, if a current-time curve were plotted it would easily .be seen thatthere are fluctuations in the current supplydue to either the rectification or the commutation of the current. This current may upon further consideration be said to consist of a constant current component and alternating current components superimposed thereon. \Vhen, such a unidirectional current is. fed through a resistance network and plate potentials are tapped therefrom, undesired results obtain; one of which, when the ther- 5 mionic tube is used in connection with a radio receiving outfit for example, manifests itself in the telephones of the receiver as as annoying hum. V

' One of the objects of this invention, therefore, is to provide means whereby this and other effects due to the fluctuations in the direct current source, are substantially eliminated.

The fluctuations in plate potential, due to the fluctuations in current in the network, in turn vary the electron flow within the tube, and hence cause hum and other objectionable noises. This may be counteracted byapplying to the input of the tube a voltage of a 40 value and phase such that, whenever a'mo-' mentary increase in plate voltage tends to increase the flow within the tube, the applied counteracting input voltage will tend to decrease the current within the tube, and vice versa. This may be accomplishedby connecting the plate and grid topoints on the ton factor of the tube.

If that is done, however, there will be no normal flow of current withinthe tubefor the reason thatthe bias of the grid will be such thatthe electron flow will be completely choked. This'in turn would mean that only the positive half of the wave applied to the input of the tube for amplfication will cause a flow within the tube and is undesirable in the case of straight amplification where both portions of an input wave should be equally amplified.

Accordingly, it isa further object of this invention to'provide means for securing a normal plate current flow, and to provide additional means in the output circuit for balancing out the harmful effects of thepotential varations caused by the fiuctuationsin the direct current source utilized for energizing the tube. a This is done by providing paths from the grid and plate of the tube to the net-- work for maintaining a desired normal current flow, and by providing another alternating currentpath as the working voutputcircuit of the tube, from its plateto the network.

connected so that it is unaffected by the network current fluctuations. v

The novel features which Ibelieve to be characterized by my invention are set forth in particularity in the appended claims, the invention itself, however, as to both'its or ganization and method of operation will best be understood by reference to thefollowing description taken in connection with the drawing in which I have indicated diagrammatcally one'circuit arrangement whereby ,my invention maybe carried into effect.

4 The invention will be more fully described hereinafter with the aid of the accompanying drawing in which I have illustrated the manner of connecting two stages of an audio frequency amplifier, for example, to a resistance network for obtaining therefrom current potentials for energizing the tubes and means for eliminating the eflects of current variation in the network from affecting the output circuits of the tubes.

The figure diagrammatically shows how the effects of fluctuations in the network 2 energized from a variable unidirectional source of current 1, may be eradicated by plate connections. For the sake of brevity only two stages of an audio frequency amplifier have been shown although it is clear that the invention is applicable to all stages of radio and audio frequency amplification. Telephones 26 and condenser 28 form an audio frequency path from the plate of tube 25 to network 2, and choke 27 forms a substantially direct current path to the network 2.- Telephones, or other signal translating devices, 26 are preferably placed in the alternating current path although they may be placed in the connection 36 between the plate and choke 27 which connection carries both the direct and alternating components.

Grid 29 is connected to point 30 in the network for obtaining a desired bias. Choke 27 is connected to net-work2 at point 31 for obtaining a desired plate potential, that is, points 30 and 31 are chosen so that tube 25 is operating on a desired point on its characteristic curve. Condenser 28 of large capacity is connected to point 32 on the network such that the voltage drop from point 32 to the midpoint of portion 33 of the network 2 across which filament 34L of tube 25 is shunted, is equal to the product of the between points'32 and the midpoint of the portion 33, the opposing plate voltage being equal in numerical value and opposite in sign to the voltage variation applied to the grid times the amplification factor of the tube. Input voltage variations through transformer 35 however, are unaffected and are readily amplified by tube 25 so as to actuate telephones 26. Similarly, the input to transformer 35 is unaffected.

It is clear, of course, that resistance 2 need not be continuous or uniform throughout its length but may be composed of several lumped resistances for the purpose of obtaining desired potential difference as indicated hereinbefore. The various taps such as 30, 30, 31, 31, 32 and 32 may be made adjustable and may be varied until desired operation of the system is had.

It is also clear that the filaments may be connected in series with the remaining portions of the network 2 and not affect the operation of the system. It is preferred, however, to place the filaments across portions of the network 2 so that should one of them burn out the filaments of the remaining tubes will remain incandescent thereby indicating the defective tube. The output circuits of the other stages'of the system should be connected similarly to that of tube 25, with the exception that the plate coupling impedance should be substituted for telephones 26. The manner of doing so is indicated clearly by the connections for tube 25. v

The variation in voltage across portions 33 and 33- will not cause any appreciable hum as the thermalinertia of each of the filaments is such as to maintain thev electron flow independent of the slight potential variations across it. v

While I have indicated and described only one system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described and that many modifications in the circuit arrangement may be used, as well as in the apparatus employed without departing from the scope of my invention as set forth in the appended claims. 7

Having thus described .my invention what I'claim is: i

1'. In apparatus of the character described, a resistance adapted to be connected to a source of direct current, an electron discharge device having its cathode connected to an intermediate point on said resistance, and having its grid and anode connected to points 7 on said resistance negative and positive respectively with respect to the cathode connection, said anode connection having a highimpedance to direct current the ratio of the potential differences between the grid and cathode and the anode and cathode being substantially equal to the reciprocal of the amplification factor of said tube and a direct current connection from the anode to a point on said network having a positive potential.

2. In apparatus of the character described, a resistance network adapted to be connected to a source of unidirectional current, a plurality of thermionic tubes having grids,

anodes and filaments, connections from the grids and filaments of the tubes to the network, and a plurality of connections from each anode to a plurality of points of differentpotential on said network, said last mentioned connectlons comprising means for se- Lin lectively passing alternating and direct current components, respectively.

3. In apparatus of the character described, a resistance network adapted to be connected to a source of unidirectional current, a plurality of thermionic tubes having grids, anodes and filaments, connections from the grids and filaments of the tubes to the network, and a plurality of connections from each anode toa plurality of points of different potential on said network, said last mentioned connections comprising means for selectively passing alternating and direct current components, respectively, the connections comprising means for passing alternating components being connected to points on the network such that the ratio of the anode-cathode potential drop on the network, to the grid-cathode potential drop on the network equals respectively the amplification factor of the respective tubes.

I. In apparatus of the character described, a direct current network, a thermionic tube, having its cathode connected to the network and its anode connected to two points on said network positive with respect to said cathode connection one of said anode connections having a high impedance to direct current and a low impedance to alternating current of audible frequency, and the other anode connection havin a high impedance to alternating current.

5. In apparatus of the character described, a direct current network, means for connecting a source of potential in series therewith, a thermionic tube having anode, cathode and grid electrodes, means for connecting said cathode in parallel with a portion of said network, means for connecting said grid electrode to a point on said network, means for connecting the anode of said tube to a point on said network such that the voltage drop between said last named point and said filament is equal to the voltage drop between the point of connection of the grid to said network multiplied by the amplification factor of the tube and means for connecting said anode to a second point on said network, said two points on the network to which the'anode is connected being of different potential.

6. In radio apparatus adapted to energize thermionic tubes, a resistance network, means ance to alternating quency.' V

7. In a cascade amplifier for audio frequency, a pair of thermionic tubes each havourrent of audible freing cathode, anode and grid electrodes, a netsaid network positive with respect to said cathode.

8. In a cascade amplifier and a direct current network, means for connecting a source of potential in series therewith, -a thermionic tube having anode, cathode and grid electrodes, means for connecting said cathode of said tube in parallel with a portion otsaid network, means for connectingthe grid electrode of said tube to :a,,po int on said network,

ardirect current path connecting the anode" of said tube to a point on said network and an alternating current path connecting said anode to a point 'onsaid network such that the voltage drop between said last named point and the cathode is equal to the voltage drop between the grid connection to said net work and the cathode. multiplied by the amplification factor of the tube.

"9. In apparatus of the character described,

a direct current network, means for connect- 1 ing a source of potential in seriestherewith, a. thermionic tube havinganode, cathode and grid electrodes, means for connecting said cathode in :parallelwith a'portion of said network, means for connecting said grid electrode to a point on said network negative with respect to said cathode, .a direct cur-l rent path connecting the anode of'said tube 'toa positive point on said network and an alternating current path connecting said an- 1 ode to a point on said network such that the voltage drop between said last named point and said cathode is equal to the voltage drop between said cathode and the point of connection of the'grid tosaid network multiplied by the-amplification factor of thetube.

10. In a cascade amplifier for audio frequency, a pair of thermionic tubes each having anode, cathode and grid electrodes, a resistance network, means for connectingthe cathode of each of said tubesin parallel with diiterent portions. of said resistance network, means for connecting the grid of each of said tubes to a'point on said resistance negative with respect to the points of connection between the cathodes and said network, a direct current path connecting the anode of each or" said tubes to: a point on saidnetwork positive iwithrespect tothe point of connection of said cathodes to saidnetwork, analternating current path connecting the anode of each of said tubes to said network at-points so chosen with respect to the cathode connection of that tube, that the voltage drop between each of said points and the respective cathode connection to said network is equal to the voltage drop between each of said grid connections and the cathode of that tube multiolied by the amplification factor of that tube.

11. In combination, a resistance network, an electron discharge tube having its cathode connected to a point on said network, means for connecting the control electrode of the tube to a point on said network more negative than said first point, means for connecting the anode of the tube to a point on said network more positive than said first point, and additional means having a high impedance to direct current but a low impedance to alternating current of audible frequency for connecting said anode to a second point on said network less positive than said first do connection point.

12. In combination, a resistance network, an electron discharge tube having its cathode connected to a point on said network, means for connecting the control electrode of the tube to a point on said network more negative than said first point, means for connecting the anode of the tube to a point on said network more positive than said first point, and additional means having a high impedance to direct current but a low im pedance to alternating current of audible frequency for connecting said anode to a second point on said network less positive than said st anode connection point,there being a greater potential difference between the said second anode connection point and said catl ode connection point than between said control electrode connection point and said cathode point. i

13. In combination, a resistance network, an electron discharge tube having its cath- WVALTER VAYN B. ROBERTS.

ode connected to a point on said network,

means for connecting the control electrode of the tube to a point on said network more negative than said first point, means for con necting the anode of the tube to a point on said network more positive than said first point, and additional means having a high innpedance to direct current but a low impedance to alternating current otaudible frequency, and including a translating device, for connecting said anodeto a second point on said network less positive than said first anode connection point.

14. In combination, a resistance network, an electron discharge tube having its cathode connected to a point on said network, means for connecting the control electrode of the tube to a point on said net-work more negative than said first point, means for connecting the anode of the tube to a point on 

